Kubernetes Liveness Check

When deploying software with Kubernetes, you need to expose a liveness HTTP request in the application. The Kubernetes default liveness HTTP endpoint is /healthz, which seems to be a Google convention, z-pages. A lot of Kubernetes deployments won’t rely on the defaults. Here is an example Kubernetes pod configuration for a liveness check at <ip>:8080/health:

apiVersion: v1
kind: Pod
metadata:
  name: liveness-http
spec:
  containers:
    - name: liveness
      image: k8s.gcr.io/liveness
      args:
        - /server
      livenessProbe:
        httpGet:
          path: '/health'
          port: 8080
        initialDelaySeconds: 3
        periodSeconds: 3

When setting up a new app to be deployed on Kubernetes, ideally, the liveness endpoint is defined in a service scaffold (this is company and framework dependent), but in the case it isn’t, you just need to add a simple HTTP handler for the route configured in the yaml file. In an express app, it could look something like this:

app.get('/health', (req, res) => {
  res.status(200).send('OK');
});

Notably, the default express scaffold doesn’t come with this route. You either need to remember to add this route or create a custom scaffold that includes it following your Kubernetes liveness check convention.